For many years radar system array antennas have been known, and have been used for the formation of sharply directive beams. Array antenna characteristics are determined by the geometric position of the radiator elements and the amplitude and phase of their individual excitations.
Later radar developments, such as the magnetron and other high powered microwave transmitters, had the effect of pushing the commonly used radar frequencies upward. At those higher frequencies, simpler antennas became practical which usually included shaped (parabolic) reflectors illuminated by horn feed or other simple primary antenna.
Next, electronic (inertialess) scanning became important for a number of reasons, including scanning speed and the capability for random or programmed beam pointing. Since the development of electronically controlled phase shifters and switches, attention in antenna design has been directed toward the array type antenna in which each radiating element can be individually electronically controlled. Controllable phase shifting devices in the phased array art provides the capability for rapidly and accurately switching beams and thus permits a radar to perform multiple functions interlaced in time, or even simultaneously. An electronically steered array radar may track a great multiplicity of targets, illuminate and/or tag a number of targets, perform wide-angle search with automatic target selection to enable selected target tracking and act as a communication system directing high gain beams toward distant receivers and/or transmitters. Accordingly, the importance of the phase scanned array is great. The text "Radar Handbook" by Merrill I. Skolnik, McGraw Hill (1970) provides a relatively current general background in respect to the subject of array antennas in general.
Other references which provide general background in the art include:
U.S. Pat. No. 2,967,301 issued Jan. 3, 1961 to Rearwin entitled, SELECTIVE DIRECTIONAL SLOTTED WAVEGUIDE ANTENNA describes a method for creating sequential beams for determining aircraft velocity relative to ground.
U.S. Pat. No. 3,423,756 issued Jan. 21, 1969, to Foldes, entitled SCANNING ANTENNA FEED describes a system wherein an electronically controlled conical scanning antenna feed is provided by an oversized waveguide having four tuned cavities mounted about the waveguide and coupled to it. The signal of the frequency to which these cavities are tuned is split into higher order modes thus resulting in the movement of the radiation phase center from the center of the antenna aperture. By tuning the four cavities in sequence to the frequency of this signal, it is conically scanned. Signals at other frequencies, if sufficiently separated from the frequency to which the cavities are tuned, continue to propagate through the waveguide without any disturbance in the waveguide.
U.S. Pat. No. 3,969,729, issued Jul. 13, 1976 to Nemet, entitled NETWORK-FED PHASED ARRAY ANTENNA SYSTEM WITH INTRINSIC RF PHASE SHIFT CAPABILITY discloses an integral element/phase shifter for use in a phase scanned array. A non-resonant waveguide or stripline type transmission line series force feeds the elements of an array. Four RF diodes are arranged in connection within the slots of a symmetrical slot pattern in the outer conductive wall of the transmission line to vary the coupling therefrom through the slots to the aperture of each individual antenna element. Each diode thus controls the contribution of energy from each of the slots, at a corresponding phase, to the individual element aperture and thus determines the net phase of the said aperture.
U.S. Pat. No. 4,041,501 issued, Aug. 9, 1977 to Frazeta et al., entitled LIMITED SCAN ARRAYANTENNA SYSTEMS WITH SHARP CUTOFF OF ELEMENT PATTERN discloses array antenna systems wherein the effective element pattern is modified by means of coupling circuits to closely conform to the ideal element pattern required for radiating the antenna beam within a selected angular region of space. Use of the coupling circuits in the embodiment of a scanning beam antenna significantly reduces the number of phase shifters required.
U.S. Pat. No. 4,099,181, issued Jul. 4, 1978, to Scillieri et al, entitled FLAT RADAR ANTENNA discloses a flat radar antenna for radar apparatus comprising a plurality of aligned radiating elements disposed in parallel rows, in which the quantity of energy flowing between each one of said elements and the radar apparatus can be adjusted, characterized in that said radiating elements are waveguides with coplanar radiating faces, said waveguides being grouped according to four quadrants, each one of said quadrants being connected with the radar apparatus by means of a feed device adapted to take on one or two conditions, one in which it feeds all the waveguides in the quadrant and the other in which it feeds only the rows nearest to the center of the antenna excluding the other waveguides in the quadrant, means being provided for the four feed devices to take on at the same time the same condition, so that the radar antenna emits a radar beam which is symmetrical relatively to the center of the antenna, and having a different configuration according to the condition of the feed devices.
U.S. Pat. No. 4,595,926, issued Jun. 17, 1986 to Kobus et al. entitled DUAL SPACE FED PARALLEL PLATE LENS ANTENNA BEAMFORMING SYSTEM describes a beamforming system for a linear phased array antenna system which can be used in a nonpulse transceiver, comprising a pair of series connected parallel plate constrained unfocused lenses which provide a suitable amplitude taper for the linear array to yield a low sidelobe radiation pattern. Digital phase shifters are used for beam steering purposes and the unfocused lenses de-correlate the quantization errors caused by the use of such phase shifters.
U.S. Pat. No. 3,546,699, issued Dec. 8, 1970 to Smith, entitled SCANNING ANTENNA SYSTEM discloses a scanning antenna system comprising a fixed array of separate sources of in-phase electromagnetic energy arranged in the arc of a circle, a transducer having an arcuate input contour matching and adjacent to the arc, a linear output contour, and transmission properties such that all of the output energy radiated by the transducer is in phase, and means for rotating the transducer in the plane of the circle about the center of the circle.
U.S. Pat. No. 5,283,587, issued Feb. 1, 1994 to Hirshfield et al. entitled ACTIVE TRANSMIT PHASED ARRAY ANTENNA discloses an antenna for generating multiple independent simultaneous antenna beams to illuminate desired regions while not illuminating other regions. The size and shape of the regions is a function of the size and number of elements populating the array and the number of beams is a function of the number of beam forming networks feeding the array. All the elements of the array are operated at the same amplitude level and beam shapes and directions are determined by the phase settings. There is no indication of how to achieve an amplitude taper in this system. In some applications, phase only taper is insufficient to achieve necessary beam shapes and suppress sidelobes.
It would be desirable to be able to provide an antenna array where each of the amplifiers are provided with nearly identical output characteristics to limit the adverse phase effects resulting from devices with differing internal structures, while permitting an effective tapering of both amplitude and phase for each of the elements in the array.